powerful celebration 100 years in the making. that s a once in a lifetime experience. this is where we have to be on the centennial. reporter: leading former guards to arlington s tomb of the unknown soldier to france for the 100th anniversary of this, the october 24th, 1921 selection of an american world war i soldier killed in france representing thousands that never came home. that soldier returned to the u.s. and buried at arlington on what we now call veterans day. it is something that touches your life forever. reporter: this pilgrimage an emotional experience for will, a korean war vet and former tomb guard. when i get here and look around at the scale of the war, world war i, that just i can t get my brain around it. reporter: there are tens of thousands of american soldiers from world war i buried all over europe, but this journey was intended to honor one soldier who represents all of the unknowns the small city of chalons-en-champagne is where the unknown selec